Delayed fuel and post ignition timed burner control system

ABSTRACT

A SUBSTANTIALLY ALL SOLID STATE CONTROL SYSTEM WHICH IS ADAPTED TO BE CONNECTED TO CONTROL A FUEL BURNER MEANS IS DISCLOSED AND PROVIDES A DELAYED FUEL AND POST-IGNITION TIMING PERIOD USING A HEATER OPERATED BIMETAL SWITCH. THE SYSTEM IS ADAPTED TO BE ENERGIZED THROUGH A LINE VOLTAGE THERMOSTAT TO PROVIDE POWER TO A FUEL BURNER MEANS WHICH MAY INCLUDE TWO STAGES OF FUEL CONTROL, ALONG WITH AN IGNITION MEANS AND FLAME DETECTION MEANS. THE SYSTEM INCLUDES A DIODE CONNECTED BETWEEN A TRIAC, WHICH CONTROLS THE FIRST STAGE OF FUEL, AND THE SAFETY SWITCH HEATER THAT IS NORMALLY CONTAINED IN SUCH A SYSTEM. THIS DIODE PROVIDES A SAFE MODE OF FAILURE IN THE EVENT THE TRIAC SHORT CIRCUITS AND ALSO PROVIDES A CURRENT PATH FOR SAFETY SWITCH HEATER CURRENT IN THE EVENT OF A FLAME FAILURE DURING NORMAL OPERATION.

United States Patent 3,671,169 DELAYED FUEL AND POST IGNITION TIMED BURNER CONTROL SYSTEM Roland L. Hron, Bloomington, Minn., and Franciscus A.

Jannink, Sleen, Netherlands, assignors to Honeywell Inc., Minneapolis, Minn.

Filed Mar. 15, 1971, Ser. No. 124,129 Int. Cl. F23n 5/20 U.S. Cl. 431-67 8 Claims ABSTRACT OF THE DISCLOSURE A substantially all solid state control system which is adapted to be connected to control a fuel burner means is disclosed and provides a delayed fuel and post-ignition timing period using a heater operated bimetal switch. The system is adapted to be energized through a line voltage thermostat to provide power to a fuel burner means which may include two stages of fuel control, along with an ignition means and flame detection means. The system includes a diode connected between a Triac, which controls the first stage of fuel, and the safety switch heater that is normally contained in such a system. This diode provides a safe mode of failure in the event the Triac short circuits and also provides a current path for safety switch heater current in the event of a flame failure during normal operation.

CROSS REFERENCE TO RELATED APPLICATIONS The present application relates to a United States patent application, filed on even date with the present application, directed to a photoelectric latching relay disclosed but not claimed in the present application. The related application is filed in the name of Roland L. Hron and is assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION In the operation of fuel burner means, safety and reliability are essential. Components which normally are reliable sometimes can malfunction in a manner to create a hazardous operating condition of the fuel burner means. In the present invention a system has been disclosed which has been designed so that any failure of a component will create a failure mode that will not create a hazardous condition. By this it is meant, that any failure is such as to cause the system to promptly turn itself off or to turn itself off after the end of a normal cycle of burner operation. The burner cannot be restarted with the admission of fuel which is not properly ignited and this ignition subsequently sensed in the burner.

SUMMARY OF THE INVENTION The present invention is directed to a fuel burner control system that is adapted to be connected to a fuel burner means, and a condition sensing means or thermostat, and which is capable of reliable operation through the use of solid state components. The circuit configuration is arranged so as to provide for delayed fuel and postignition timing through the use of a thermal time switch means. The circuit further contains a diode which links one of the solid state switch means, in the form of a Triac, to a conventional safety switch heater so that any failure in the circuit causes the overall system to fail in a safe manner. This diode also provides for safety switch heater operation upon flame failure. A safe failure manner or mode is one in which the burner means is prevented from being placed in operation or in which a normal operation is terminated by an opening of a safety switch 3,671,159 Patented June 20, 1972 "ice which locks the system out by removing power from the system until the system is manually placed back into operation.

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT A conductor 10 and terminal 9 at conductor 11 are connected to a conventional source of alternating current voltage for energizing the fuel burner control system generally disclosed at 1'2 and which is adapted to be connected to a fuel burner means 13. Conductor 10 is connected through a limit control 14, such as a boiler low water cut out or temperature responsive switch, as is wellknown in the art. The limit 14 is in turn connected to terminal 15, a fuse 16, and a normally closed safety switch contact 17 that is thermally linked at 20' to a safety switch heater 21 within the fuel burner control system 12. The safety switch heater 21 and the safety switch 17 are of a conventional design wherein the heater 21 opens the contact 17 in the event of an unsafe condition and normally is reset manually. Safety switch 17 is in turn connected to a terminal 22 that connects through a condition sensing means 23 (shown as a conventional thermostat) to a further terminal 24. When the condition sensing means or thermostat 23 is closed, power is supplied to the fuel burner control system 12 and the fuel burner means 13.

The fuel burner means 13 has a number of terminals 25, 26, 27, 28, 30 and 31 which allow the fuel burner means 13 to be connected to the fuel burner control system 12. Terminal 25 is connected to the terminal 24 by conductor 32 and supplies energy to a fan 33 that is also connected to terminal 30 which in turn is connected to conductor 11 to supply alternating current to the fan 33 as soon as the thermostat 23 closes.

A two-stage fuel burner 34 is disclosed having two valves 35 and 36 which supply fuel to the burner 34 from a common supply source 37. The valve 35 has associated with it a solenoid actuator 38, while the valve 36 has a solenoid actuator 39. Valve actuator 39 can be placed in parallel with fan 33 across terminals 27 and 30 for a preignition hookup. The solenoid actuators and valves are of conventional design and admit fuel to the burner 34 by the solenoid 39 first becoming energized thereby opening valve 36, and the subsequent opening of valve 35 by the energization of the solenoid 38. Also included in the fuel burner means 13 is a spark ignition transformer 40 having a spark gap 41 for ignition of fuel from the burner 34. The transformer 40 has a primary winding 42 that is connected between the terminals '28 and 30 of the fuel burner means 13.

To complete the fuel burner means 13, a flame sensing device or photocell 43 is provided, and the photocell 43, is connected between the terminals 31 and 30 of the fuel burner means 13. The photocell 43 has a relatively high resistance when no flame exists at the burner 34, and has a very low resistance when a flame is present at the burner 34. The photocell is of a conventional design. The photocell can \be replaced by any type of flame sensing device which would provide two levels of output depending on whether a flame exists or does not exist at the burner 34.

The terminals 9, 15, 22, and 24 provide input terminals for the fuel burner control system and are adapted for easy connection to conventional equipment. Terminals 25 through 31 provide means to adapt the connection of the fuel burner control system 12 to a fuel burner means 13, and all of the equipment in the fuel burner means 13 and connected to the input terminals are conventional in nature and do not form part of the present invention. The invention is in the fuel burner control system 12 which is adapted to be connected to the terminals set forth above.

In the fuel burner control system 12, a main supply conductor 45 is provided which connects to terminal 24 and provides energy to a bias means made up of conductor 46, resistor 47, and capacitor 48. The bias circuit means has a junction point 50 that is connected by conductor 51 to terminal 31 and thereby to the photocell 43. The point 50 is also connected through a Diac or voltage breakdown device 52 to a gate 53 of a Triac Q1. The Triac Q1 is connected by conductor 54 to a conductor 55 that joins the terminals 9* and 30 to supply one side of the line 11 to the fuel burner means 13. The other side of the Triac Q1 is connected by conductor 56 to a common point 57, a conductor 58 and timer heater 60, which forms part of a time switch means 61. The time switch means 61 includes a double throw switch having terminals 62, 63, and a common terminal 64 that is in turn connected at 65 to conductor 45. The time switch means 61 includes in its structure a bimetal 59 which is responsive to the timer heater 60 to position the double throw switch between the position shown with terminals 63 and 64 connected for a delayed fuel period when the timer heater 60 is cold. The switch means 61 would be closed between terminals 64 and 62 for a postignition timing function when the timer heater 60 is sufficiently hot to warp the bimetal 59' to operate the switch mechanism.

The switch terminal 62 for post-ignition is connected by a conductor 66 through a diode 67 to the previously mentioned safety switch heater 21.. This forms part of a main circuit means for the Triac Q1. The safety switch heater 21 in turn is connected to a radiation operated latching relay means 70' of a rather unusual nature. The relay means 70 includes an incandescent light bulb 71 that is connected between the safety switch heater 21 and the junction 57 in series circuit with the Triac Q1. Radiation emitted from the light bulb 71 falls on a radiation responsive means or photoresistor 72, such as a cadmium sulfide photocell, that is also subject to radiation from a neon voltage breakdown type bulb 73 that forms part of the relay means 70. The neon bulb 73 is connected at a common point 74 to the terminal 27. The other side of the neon bulb 73 is connected by conductor 75 through a resistor 76 to conductor 55. The operation of the neon bulb 73 and therelay means 70 will be described in detail in the subsequent specification. The common point 74 is connected by conductor 80 through a Triac Q3 and conductor 81 to the conductor 45 for a supply of power to the neon bulb 73 and to the terminal 27 when the Triac Q3 is in conduction. A gate 83 of the Triac Q3 is connected by conductor 84 to the photoresponsive impedance 72.

To complete this portion of the circuit, a diode 85 is connected between the conductor 80 and the diode 67 at the point where it joins the safety switch heater 21. The diode 85 provides a unique protective function to provide a fail-safe mode of operation in the event that the Triac Q3 should become short circuited and this function will be described in connection with the operation of the overall system. It also provides a current path for the safety switch 21 in case of flame failure after the control has gone through its normal startup and the timer switch means 61 has returned to the cold (delayed fuel) position. Flame failure will cause the safety switch 21 to start heating immediately.

The burner control system 12 has a capacitor 86 and resistor 87 between the junction 57 and a gate 90 of a Triac Q2. A Triac Q2 is connected by conductor 91 to conductor 45 and by conductor 92 to terminal 28 of the fuel burner means 13'. To provide for a post-ignition function and to complete the described circuitry, a diode 93 is connected between the switch terminal 62 and the terminal 28 of the fuel burner means 13 to provide for half wave energization of the transformer 40 in the fuel burner means 13 during a portion of the operating cycle of the control system.

OPERATION With an alternating current potential on conductors 10 and 11 and the thermostat 23 open, the system is in a standby condition awaiting normal operation. The closing of the thermostat 23 applies power on conductor 32 directly to the fan 33 to start the fan into operation. At this same time energy is supplied to the main circuit means and the bias circuit means to provide a voltage at point 50 to trigger the Triac Q1 into conduction. The Triac Q1 conducts through the time switch means 61 by conducting through conductor 65 and the timer heater 60 (in the position shown in the drawing). This operation provides a triggering pulse from the junction 57 through the capacitor 86 and the resistor 87 to the gate of Triac Q2 and causes the Triac Q2 to be conductive through the primary winding 42 of the transformer 40. The operation of Triacs Q1 and Q2 simultaneously thereby starts a timing function by heating the timer heater 60, and starts a spark in the fuel burner means 13 across the spark gap 41.

The timer heater 60 operates for approximately 10 to 20 seconds before the heat generated is sufficient to cause the time switch means 61 to switch so that terminals 62 and 64 are connected by the time switch means 61. This immediately deenergizes the timer heater 60, but provides a current through the conductor 66 and the diode 67 along with the safety switch heater 21 to the bulb 71. Since the Triac Q1 still has a bias supplied from the junction 50, it remains in conduction thereby drawing current through the bulb 71 lighting that bulb. This current flow starts the heating of the safety switch heater 21, as well as providing a radiation from the bulb 71 which is sensed by the photoresistor 72. The photoresistor 72 changes value to provide a trigger pulse for the Triac Q3. This trigger pulse turns the Triac Q3 on and current is then conducted through the neon bulb 73 along with a second path which includes the terminal 27 of the fuel burner means 13 and the solenoid 39 of the valve 36. The current flowing through the solenoid 39 opens the valve 36 and allows gas or oil to flow to the burner 34 for ignition by the spark being generated at the gap 41.

The operation of the Triac Q3 causes the neon tube 73 to generate a radiation which falls on the photoresistive resistor 72 to in effect latch the Triac Q3 into conduction. This is accomplished by providing a photoresistor 72 which has a time constant longer than the pulses per second that flow through the neon tube 73 at 60 hertz. If the time constant of the resistor 72 is sufliciently long the pulses of light occurring at 120 cycles per second from the neon bulb appear to be a continuous light flowing to the photoresistive element 72 thereby keeping the Triac Q3 in conduction. The initial light or radiation being generated from the bulb 71 acts as a pull in for the solid state or photorelay means '70 while the light or radiation being generated by the conduction through the neon bulb 73 acts to latch this relay mechanism into operation. The relay means 70 therefore is a form of solid state relay that contains no contacts, and due to the selection of components has an exceedingly long and reliable life.

With the time switch means 61 in the position where terminals 64 and 62 are connected, the 'valve 36 is open and full wave energy is being supplied to the primary winding 42 of the spark transformer 40 so that a spark is generated. As soon as the spark ignites the fuel flowing from the burner 34, the photocell 43 senses the existence of flame and its impedance changes to a relatively low value. The photocell 43 is connected across the capacitor 48 in the bias circuit means for the Triac Q1 and this relatively low value tends to short out the gate signal to the Triac Q1 thereby turning the Triac Q1 off. As soon as the Triac Q1 is turned off no gating signal is available for Triac Q2 and it also turns off. This also removes the flow of current through the bulb 71 but the solid state relay means 70 remains energized due to the light emitted by the neon tube 73. As soon as the Triac Q1 turns off, there is no current flowing in the safety switch heater 21 thereby eliminating the possibility that the device will go out on safety as a flame has been sensed.

In order to provide a post-ignition timing function, a half wave circuit is provided through the diode 93 and through the primary winding 42 when the time switch means 61 is in the right hand position. This half wave energy provides an adequate spark to guarantee the continued ignition of the fuel from the burner 34.

After a cooling time interval for the timer heater 60, the time switch means 61 switches back to the left hand position, as shown in the drawing. The system does not start again as it did at the outset since the photocell 43 secs flame and effectively shorts out the gate signal to Triac Q1. The switching of the time switch means 61 to the left position substantially removes a short circuit from the solenoid 38 of the second stage of fuel. The removal of this short circuit, in the form of the removal of the diode 93 from the circuit, allows the second stage of fuel to be energized by the solenoid 38 being energized to open valve 35 thereby increasing the fuel flow to the burner 34. The second stage disclosed is an auxiliary or additional feature and may or may not be used in certain forms of burner installations.

In the event of the short circuiting of any of the Triacs Q1, Q2, or Q3, a safe failure mode is established in the present system. The shorting of the Triac Q11 causes the system to become inoperative by the safety switch heater remaining in the system after the operation of the photocell detecting flame and therefore the system locks itself out on safety. The shorting of the Triac Q2 provides a constant ignition spark at the burner and any admission of fuel to the burner would be ignited for proper operation. The only component which could have caused trouble upon shorting was disclosed as the Triac Q3. The shorting of Triac Q3- could have caused an unsafe mode of operation were it not for the diode '85. In the event that the Triac Q3 short circuits, the current drawn by the diode 85 upon the operation of the Triac Q1 causes current to flow through the safety switch heater 21 and would cause the system to shut down by the safety switch 17 opening. Also, in the event of flame failure when operating, the diode 85 provides a current path to heater 2:1 to cause safety switch 17 to open.

The present system discloses a substantially all solid state fuel burner control system that is adapted to be connected to a fuel burner means and wherein component failures cause a safe operating condition or a safety shut down that normally requires manual reset and therefore proper service attention before the system can be placed back into operation.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. A fuel burner control system adapted to be connected to fuel burner means having ignition means, fuel supply means, and flame sensing means, with said control system further adapted to respond to condition sensing means including: time switch means and bias circuit means connected to operatively energize first solid state switch means upon application of electrical power to said system by operation of said condition sensing means; second solid state switch means connected to be operatively energized through said ignition means upon operation of said first solid state switch means; said time switch means switching after a timed interval to energize both of said solid state switch means through alternate circuit means including safety switch timer means and relay means; said alternate circuit means providing an energizing path for said solid state switch means while maintaining said ignition means energized; and third solid state switch means operated by said relay means to in turn operate said fuel supply means to admit fuel to said fuel burner means with said relay means latching itself into an energized condition by current conduction through said third solid state switch means; said flame sensing means adapted to be connected to said bias circuit means to change a bias to said first solid state switch means to deenergize said first solid state switch means and thereby deenergize said safety switch timer means upon the advent of flame in said burner means; said time switch means resetting itself to its initial condition there by de-energizing said ignition means; said relay means remaining latched to maintain the operation of said burner means as long as said condition sensing means remains operated to supply electrical energy to said control system.

2. A fuel burner control system as described in claim 1 wherein said time switch includes a heater and a heat responsive double throw switch operated by said heater with said heater connected to said first solid state switch means and energized upon application of electric power to said system.

3. A fuel burner control system as described in claim 2 wherein all of said solid state switch means are T riacs.

4. A fuel burner control system as described in claim 1 wherein said alternate circuit means and said third solid state switch means are connected by diode means so that said safety switch timer means and said relay means are energized in the event of an abnormal condition of operation of said system to in turn operate said safety switch timer means to deenergize said system.

5. A fuel burner control system as described in claim 4 wherein said safety switch timer means includes an electric heater and a normally closed bimetal operated switch connected in series with said condition sensing means.

6. A fuel burner control system as described in claim 5 wherein said time switch means includes a heater and a heat responsive double throw switch operated by said heater with said heater connected to said first solid state switch means and energized upon application of electric power to said system.

7. A fuel burner control system as described in claim 6 wherein all of said solid state switch means are Triacs.

8. A fuel burner control system as described in claim 7 wherein fuel supply means is a two-stage fuel supply means having a second stage connected in parallel circuit means to said third Triac and operative when said third Triac ceases to conduct upon said timer switch means resetting itself to its initial condition deenergizing said ignition means.

References Cited UNITED STATES PATENTS 3,549,088 12/1970 Obenhaus et al. 431-67 3,600,117 8/1971 I-Iirsbrunner 431-66 EDWARD G. FAVORS, Primary Examiner 

